How can I set a vector in C++ and all its data at the same time?

Question

I wrote some JavaScript code but now I want to translate it to C++ because of perfomance, but my knowledge of C++ is low.

In JavaScript I can do:

var arr=[[['à','á'],['è','é'],['ì','í'],['ò','ó'],['ù','ú']],['a','e','i','o','u']];

How can I do something like that in C++? Must I do

vector<vector<char>> arr;

and then set each element manually?

arr[0][0]='à';
arr[0][1]='á';
...

FYI: C++'s `char` type is not good for Unicode symbols. – qehgt Jul 17 '12 at 16:14 — qehgt, Jul 17 '12 at 16:14
But works fine with ISO-8859-1 – Martin York Jul 17 '12 at 16:22 — Martin York, Jul 17 '12 at 16:22

score 7 · Accepted Answer · answered Jul 17 '12 at 16:12

7

Yes, it's at least a bit more work unless you have C++11, which adds the possibility of constructors taking an initializer list:

std::vector<std::vector<char>> arr {{'a', 'b'}, {'c', 'd', 'e'}, {'f'}};

You might also consider replacing std::vector<char> with std::string.

answered Jul 17 '12 at 16:12

chris

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Thanks for answering so fast.I didn't know C++11. Do you know how can I use it in Dev-C++? – Oriol Jul 17 '12 at 16:48
@Oriol, IIRC Dev-C++'s version of GCC is pretty old. If it's too old, you'll have to upgrade it (my personal favourite is http://nuwen.net/mingw.html). Also, you must compile with `-std=c++11` or `-std=c++0x`. As for the IDE, [CodeBlocks](http://www.codeblocks.org/) is a good step up from Dev-C++. I'm familiar with upgrading GCC on there; all I have to do is replace the `MinGW` folder with the new one. – chris Jul 17 '12 at 16:53
Thanks! I have installed minGW 64 bits (minGW 32 bits threw errors) and now it works. – Oriol Jul 17 '12 at 19:14

score 2 · Answer 2 · answered Jul 17 '12 at 16:18

This will work for C++11

std::vector<std::vector<char>> var arr={{'à','á'},{'è','é'},{'ì','í'},{'ò','ó'},{'ù','ú'},{'a','e','i','o','u'}};
// Note it is changed from the original I removed one level of nesting from part of the array.

If you are using C++03.
Then you need to change things slightly.

std::string var[] = {"àá'", "èé", "ìí", "òó", "ùú", "aeiou"};

The types have changes but it has the same affect and access to the object var is unchanged.

score 2 · Answer 3 · answered Jul 17 '12 at 16:21

Alternatively, you could use std::vector< std::pair< char, char > >.

Note, that you cannot use operator[](ie. call arr[0] or arr[0][0] on an empty vector (since the requested elements are not there, you access invalid memory which (hopefully) will crash your program). Add elements to a vector with push_back(...):

vector< pair< char, char > > arr;
arr.push_back( make_pair( 'à','á' ) );
arr.push_back( make_pair( 'è','é' ) );
arr.push_back( make_pair( 'ì','í' ) );
arr.push_back( make_pair( 'ò','ó' ) );
arr.push_back( make_pair( 'ò','ó' ) );
arr.push_back( make_pair( 'ù','ú' ) );

Depending on what you want to do, std::map< char, char > might be useful for you as well. It will allow you to access elements using the first type as a key, eg.

std::map<char, char > mymap;
mymap['à'] = 'á';
// will print "Element à = à"
cout << "Element à = " <<  mymap['à']  << endl;

score 1 · Answer 4 · answered Jul 17 '12 at 16:12

1

Unfortunately you can't initialize a vector as an array. However, you can initialize a vector with an array. For a single vector:

static const int arr[] = {1,2,3,4};
vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

Initializing a vector of vectors is a little tricky, but you can do it in a cycle either like above, or like this: (pseudocode):

for( int i =0; i < something; i++ )//the outer vector
{
    vector.pushBack( std::vector<int> );
    for( int j =0; j < somethingElse; j++)
        vector[i].push_back(j);
}

answered Jul 17 '12 at 16:12

SingerOfTheFall

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1

Or better, `std::vector vec(std::begin(arr), std::end(arr));` – Seth Carnegie Jul 17 '12 at 16:13
@SethCarnegie, If you have C++11, you might as well use my solution. This fits the bill perfectly for C++03. – chris Jul 17 '12 at 16:14
@chris are `begin` and `end` C++11 only? I thought C++03 had references to arrays too. If it's just that they don't come in `std` then you can write your own. – Seth Carnegie Jul 17 '12 at 16:14
@chris even if you use C++03, it pays to have your own `begin` and `end` for arrays. – R. Martinho Fernandes Jul 17 '12 at 16:14
@SethCarnegie, http://en.cppreference.com/w/cpp/iterator/begin. True, it's possible to make your own, though. – chris Jul 17 '12 at 16:15
@R.MartinhoFernandes and you can also make them work for STL containers as well (because if the type provides a `iterator` typedef then you don't need `decltype`) – Seth Carnegie Jul 17 '12 at 16:16

score 0 · Answer 5 · answered Jul 17 '12 at 16:15

0

Here's a code snippet using c++0x:

#include <vector>
#include <iostream>
using namespace std;

int main(){
    vector< vector<char> > v = { {'a','b','c'}, {'d','e','f'} };
    for (unsigned i=0; i<v.size(); i++){
        cout <<"Subvector: ";
        for (unsigned j=0; j<v[i].size(); j++)
            cout << v[i][j];
        cout << endl;
    }

    return 0;
}

Compile it with g++ -std=c++0x

answered Jul 17 '12 at 16:15

Guy Adini

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C++11 has [ranged-based for loops](http://en.wikipedia.org/wiki/C%2B%2B11#Range-based_for-loop) you can use to make going through it easier. – chris Jul 17 '12 at 16:16

How can I set a vector in C++ and all its data at the same time?

5 Answers5